Studying the Onset of Nuclear Collectivity beyond N=40 with Manganese Mass Measurements

The region of the nuclear chart below ⁶⁸Ni has been an area of intense experimental and theoretical effort due to the potential onset of a new "island of inversion" when crossing the harmonic oscillator subshell closure at N = 40. We have measured the masses of ^64-68Mn using TITAN's multiple-reflection time-of-flight mass spectrometer, resulting in the first precision mass measurements of ⁶⁷Mn and ⁶⁸Mn. These results are compared to ab initio calculations and modern shell model calculations and show an increase in collectivity approaching N = 40.